In the food industry a growing trend toward "light" and low-calorie can be observed. The use of too much fat and/or sugar in products is avoided. To nevertheless be able to provide food products with a sweet taste, an increasing number of sugar substitutes are becoming commercially available. Aspartame is a known example thereof. Aspartame, however, has poor organoleptic properties.
Another type of sugar substitute is formed by oligosaccharides. Oligosaccharides are molecules which consist of two or more monosaccharides such as fructose and/or glucose. The monosaccharides in oligosaccharides are linked to each other either by .beta.--(2-1) or by .beta.--(2-6) bonds. The number of monosaccharides in an oligosaccharide is indicated by means of the DP-value ("Degree of Polymerisation"). A DP-value of 3 means that the oligosaccharide is composed of three monosaccharides. Oligofructoses are oligosaccharides consisting entirely of fructose units. When an oligosaccharide also comprises one or more glucose units these will be linked by means of an .alpha.--(1-2) bond to a fructose unit. The composition of oligosaccharides is also designated with the formula G.sub.m F.sub.n, wherein G represents glucose and F fructose and wherein m equals 0 or 1 and n is an integer larger than or equal to 0. Particularly suitable oligosaccharides are those wherein m equals 1 and n is 2 to 8, preferably 2 or 3.
Oligosaccharides can hardly be hydrolysed, if at all, in the human stomach and small intestine. It is known of oligofructose that the digestive enzymes of the human have no effect on the .beta.--(2-1) and .beta.--(2-6) bond in the molecule. They therefore pass through the stomach and the small intestine without being degraded and absorbed into the body. The oligosaccharides do not however leave the body but are metabolised by the microbial flora of the large intestine. Released herein in addition to gas are volatile fatty acids which in turn again serve as an energy source for the intestinal flora. This phenomenon explains why oligosaccharides have a lower energy value for humans than free sugars such as glucose, fructose and sucrose, which are absorbed into the body. Oligosaccharides do however have sufficient sweetening power to serve as sugar substitutes.
It is further known that oligosaccharides, particularly oligofructose, have a bifidogenic effect, that is, that they stimulate the growth of Bifidobacteria in the digestive tract. Bifidobacteria protect against the development of pathogenic bacteria and thereby have a positive influence on health. In addition, oligosaccharides are nutritional fibres.
Different oligosaccharides, which are prepared in diverse ways, are already commercially available.
Oligosaccharides can be made by partial enzymatic hydrolysis of longer vegetable inulin chains. A method herefor is described for instance in European patent application 440.074.
Oligosaccharides can likewise be enzymatically synthesized. For the enzymatic production route use is made of enzymes, fructosyltransferases, which convert sucrose to a mixture of oligosaccharides and which are isolated from different micro-organisms (see Japanese Patent 80/40193).
The known production routes have a number of drawbacks however. Firstly, the known production methods are relatively expensive. In addition to the desired oligosaccharides with a chain length of 2 to about 7, in the produced mixture there also occur a comparatively large number of free sugars and oligosaccharides with a higher chain length. The drawback to many free sugars is that they result in an increase in the energy value of the mixture. Free sugars have for instance an energy content of 17 kilojoule per gram, while pure GF.sub.2 and GF.sub.3 have an energy content of 4 to 6 kilojoule per gram. In addition, free sugars cause dental decay (caries).
Conversely, oligosaccharides with too high a chain length have too little sweetening power, which causes the average sweetening power of the mixture to fall.
In contrast to some other sweeteners, such as for example Aspartame, oligosaccharides have good organoleptic properties.
It is the object of the present invention to provide an alternative production route for oligosaccharides with which the above stated drawbacks are avoided.